The present invention relates to internal antennas for use in telecommunications equipment, particularly portable radiotelephones, and a method of their manufacture.
All mobile telecommunication equipment, such as portable radiotelephones, require at least one antenna in order to be able to receive and/or transmit radio signals. Traditionally these have taken the form of structures external to the main body of the equipment.
Whip antennas were once used widely, but due to their physical size in relation to the ever smaller equipment to which they are attached, their use has diminished. Telescopic whip antennas have been used, whereby the antenna can be withdrawn into the body of the telephone when not in use, but again these are sizeable in use, and like all moving parts, are prone to damage. Coil or helical antennas offer relatively good performance in return for a small size. However, as the antenna is still external to the main body of the telephone, and usually projects from a top surface, it is prone to damage, and can reduce the aesthetic appeal of the telephone to which it is attached.
Consequently, there is an increasing desire to position the antenna internal to the main body of the telephone. Thus far, internal antennas tend to have taken the form of plate antennas positioned towards the top of the telephone, but they tend to be relatively bulky, and require extra steps in the assembly process which ultimately increases the cost of the telephone, and offer more opportunity for errors to occur.
At the same time as the desire to provide internal antennas has increased, advances in manufacturing processes have enabled more complex housings to be manufactured. A particular process known as in-mould decoration (IMD) or in-mould labelling (IML) has become more widely used as an alternative to etching, printing, painting or metallisation of external surfaces. The terms IMD and IML are sometimes used to define slightly different processes but, essentially, both involve applying a decorative feature or label into a mould before the moulding material is injected. IMD will be used throughout this specification to refer to all variants of the process.
IMD has gained favour as it is capable of producing results more cheaply than alternative techniques involving separate moulding and printing processes.
There now follows a brief description of the IMD process.
The first stage in the IMD process is the production of the carrier film which will carry the decoration which will eventually be visible on the external surface of the final product. This carrier film is normally a thin plastics material decorated with the text or drawings which will be seen on the exterior of the moulding once the process is complete. The decoration process may be performed using any suitable printing process, such as screen printing or lithography.
The carrier film is next selectively heat or vacuum formed to take on the profile of the desired finished article. The result of this process is a xe2x80x98shellxe2x80x99. It bears the external appearance of the finished article. i.e. all text or graphics is visible, but as the carrier film may only be of the order of a few hundred xcexcm thick, it is very flimsy and unsuitable for use as a mechanical housing.
The next stage takes the shells, places them in a mould where they are back-injected with a suitable moulding material. This injection moulding stage may use a moulding material which is identical with the carrier film material, or other materials having different properties may be used. Example materials used in the injection moulding process may be rubbers or plastics having a variety of different characteristics.
The completed part is now more mechanically robust, and bears the desired external decoration which is visible beneath the carrier film. Importantly, the carrier film and moulding material are now effectively fused together, ensuring that the decoration is protected, since the protective carrier film can not be peeled away.
An alternative to pre-forming the carrier film is to insert the film into the mould in its un-formed, flat, state. The pressure of the injection moulding process then forces the film into the mould, and achieves the same end result. A benefit of this process is that the carrier film may be loaded into the mould via continuous roll feed, leading to improved automation of the process.
A further alternative in both cases described above is that the carrier film may be of a type which is discarded after the moulding is completed, i.e. it does not form part of the finished moulded part. In this case, the carrier film simply provides a means of applying the decoration or label to the moulding. The decoration is transferred to the moulded part during the injection moulding process. The finished moulded part then bears the decoration exposed on its surface.
According to a first aspect of the present invention, there is provided a method of producing an antenna, wherein said antenna is incorporated into a unitary housing element of an apparatus, comprising the steps of: printing onto a first surface of a carrier film, using conductive ink, the antenna; inserting said carrier film into a mould; and injecting moulding material into the mould.
According to a second aspect of the present invention, there is provided a method of producing an antenna, comprising the steps of: printing onto a first surface of a carrier film, using conductive ink, the antenna; inserting said carrier film into a mould; and injecting moulding material into the mould.
The housing element may be a rear cover for a mobile telephone.
Alternatively, the housing element may form an enclosure or any constituent part, either internal or external, for use in any part of any portable telecommunications equipment.
The method may be used to produce a discrete antenna part which is then fitted into a housing for an apparatus.
An advantage of the method is that it may be configured to produce a housing with a printed antenna disposed on an interior or an exterior surface. The surface may or may not be protected by the retention of the carrier film.
Advantageously, if the carrier film is retained to form an integral part of the housing element, this offers protection to the printed antenna from the wear and tear normally encountered during everyday use.
The characteristics of the antenna can be advantageously altered through use of a moulding material which has a relatively high dielectric constant (∈). Use of such a substrate allows smaller physical antennas to be used.
The carrier film may be printed on both surfaces. This allows graphic and/or text designs to be printed onto the side of the film opposite the antenna. The graphic or text design may then be visible from the exterior of the telephone.
In an advantageous development, the pressure and temperature experienced during the IMD process acts to increase the conductivity of the printed antenna above that which would otherwise be possible if the conductive ink were cured in the usual way.
An advantage of using the IMD process to produce housings incorporating printed antennas is that the antenna design may be easily and inexpensively varied without incurring major costs in changing production tooling. The mould design can remain unaltered: the only change needed is to the screen printing of the antenna on the carrier film.
According to a third aspect of the present invention, there is provided a unitary housing element for a portable telecommunications apparatus, said housing element comprising an antenna, wherein said antenna comprises an element composed of conductive ink, and said antenna is disposed between an outer surface of said housing element and an inner surface of said housing element.
According to a fourth aspect of the present invention, there is provided a unitary housing element for a portable telecommunications apparatus, said housing element comprising a first surface, a second surface and an antenna, wherein said first surface is defined by a film, said second surface is defined by a moulding material, and said antenna is printed onto a first surface of said film using conductive ink.